package test.examation;

import java.util.Scanner;

public class 网易 {
    public static void main(String[] args) {
        m1();
        //m2();
        //m3();
        //m4();
    }

    private static void m1() {
        //数组中每个数拆分后，最多的素数个数
        //https://blog.csdn.net/DebugMyself/article/details/107884778

        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long res = 0;
        for (int i = 0; i < n; i++) {
            long ai = sc.nextLong();
            if (ai != 1){
                res += ai/2;
            }
        }
        System.out.println(res);



    }
    private static void m2() {
        System.out.println();
    }
    private static void m3() {
        System.out.println();
    }
    private static void m4() {
        System.out.println();
    }
}
